456 
The Philippine Journal of Science 
1921 
DETECTION OF ISOSPORA INFECTIONS 
Having had the opportunity to study the cysts of Isospora 
hominis it is hard for me to escape the conclusion that many 
infections with this organism have been overlooked and that the 
infection is probably more common than present reports would 
indicate. It is also a fact, to which some significance may be 
attached, that the present geographical distribution of I. hominis 
corresponds rather closely to the geographical distribution of 
protozoologists experienced in coprology. That point, however, 
will be discussed later. 
The difficulties in diagnosis are several. The oocysts are ex- 
ceedingly transparent and the protoplasm is often so widely 
separated from their inner aspects that the cysts are practically 
invisible under the powers ordinarily employed by experienced 
microscopists in searching preparations of faces. Then, the 
oval to rounded contour of the zygotes and sporoblasts and their 
greenish coloration render it extremely difficult to avoid mistak- 
ing them for some of the small plant forms so common in faces. 
After one has studied these cysts for a while, under high as 
well as low powers, it becomes somewhat easier to pick them up 
under the low dry objective; but one has to have the experience 
first. However, the recognition of these cysts in any stage of 
development affords no real difficulty to any person who has 
had previous experience with the coccidia. It is the tyro, who 
has not studied the coccidia, who is likely to* miss the cases. 
Two points should be carried in mind by those searching for 
these cysts. Preparations should be exceedingly thin and well 
diluted with water — even thinner than the preparations usually 
made for the detection of intestinal protozoa and the ova of 
parasitic worms. The light should be well regulated — that is 
to say, carefully cut down, but not too much. Under these 
conditions the outline of the oocyst may be visible even at the 
lowest magnifications ordinarily employed in work with faeces; 
that is, 100 diameters. India ink, diluted about one-half with 
water, and Donaldson’s iodine-eosin mixture I have found useful 
in picking up cysts, for their clear, oval shape in these fluids 
sharply differentiates them from other objects in the prepara- 
tion. The ink and: the iodine-eosin mixtures should not be used 
when it is desired to make camera lucida drawings or measure- 
ments of the cysts, for I find the fluid flows over the rounded 
ends of the cysts and obscures their outlines. The cysts come 
down nicely on concentration by the method of Cropper and 
